The present invention relates to a two-component safety injection syringe for medical and research purposes and more particularly to a device designed to separately store a medicament and a solvent therefor until a time just prior to injection when the two substances are mixed and then injected.
It is well known in the medical field that the shelf life of particular pharmaceutically or medically active substances is increased when the active substance is stored in a dry form or in stable but non-injectable solution form prior to injection. Many drugs now being marketed or being developed for marketing are not stable in their deliverable solutions for a sufficient period of time to allow for commercial distribution or have shelf lives which are unacceptably short. Among these pharmaceuticals are epinephrine, which is used to treat severe allergic and anaphylactic reactions, and cyclophosphamide, an anti-cancer substance. Other pharmaceutically active substances such as urokinase, which is used for dissolving blood clots, and glucagon, which is used for treating hypoglycemia, are stable only in dry powder forms. Papaverine, which is optimally stored in solution at very acidic pH levels (in the range 2.0-2.8) must be mixed with a physiologically acceptable solvent immediately prior to injection to avoid the painful and destructive effects associated with acidic solutions. Other medically active substances which do not store well in forms which can be easily administered are adenosine triphosphate (available from Genentech) and Prostaglandin-E which has a shelf life of only 24 hours when mixed for infusion.
However, storage of a medically active substance in a stable non-injectable form necessitates the pre-injection mixing of the substance with a medically acceptable solvent. Therefore, separate containers for solvent and solute are generally used. However, this method of pre-injection mixing is inconvenient because it requires more than one container. The use of more than one container is also undesirable because judgement on the part of the person mixing the medication is required to use amounts which result in an appropriate dosage and also because of the problems surrounding the difficulties in maintaining sterility when materials from two or more separate containers are mixed.
Thus, it can be seen that a need exists for injection devices which increase the shelf-life of particular pharmaceuticals by separately storing the various components of certain medicaments for a commercially acceptable period of time until a time just prior to injection. A related need is for devices which increase those shelf-lives and which require a minimum of preparation to insure a dependable and correct dosage administration. The fulfillment of such need will permit the commercial availability of many pharmaceuticals which have been heretofore available only directly from professional medical personnel.
In an attempt to solve these problems, a number of wet-dry syringes which incorporate both solvent and medically active solute in the same cartridge to be mixed just prior to injection have been developed. U.S. Pat. No. 4,689,042 to Sarnoff et al. shows a two-barreled syringe wherein the solid medicament and liquid solvent are stored in separate container portions of the device. Pre-injection mixing and injection in Sarnoff are controlled by a number of biasing springs which sequentially operate by way of releasing mechanisms to propel the solvent from one compartment into a dry medicament-containing compartment via communicating passages. The entire apparatus is then agitated by the operator to mix the medicament and solvent prior to the injection. The operator then places the injection needle into target tissue and actuates an injection mechanism which propels the mixed medicament into the subject. Sarnoff is a complex mechanism employing many components and requiring several discrete operating steps to use.
Similarly, U.S. Pat. No. 4,755,169, also to Sarnoff et al. discloses a multi-compartmented stacked syringe-within-a-syringe assembly wherein a biasing spring propels a mixing/injection piston and primary needle to rupture a seal between the respective medicament component compartments of the device. After agitation of the device and insertion of the injection needle into a target site by the operator, the biasing spring is again actuated to drive a second piston which propels the mixed medicament into the subject. Although somewhat simpler than the device of the '042 Sarnoff patent, the invention of the '169 patent is also a complex mechanism employing many components and requiring several discrete operating steps to use.
U.S. Pat. No. 4,328,802 to Curley et al. discloses a wet-dry syringe and connected vial which are separated during use and wherein the piston portion of the syringe, being biased by a spring, is actuated to inject the solvent into the solute vial whereby mixing occurs. Manual aspiration into the syringe is then necessitated to charge the syringe with the mixed medicament/solvent solution. Removal of the syringe portion from the syringe/vial assembly is required prior to injection into the subject.
Other two-chambered syringes are marketed under the tradename Variject, manufactured by Bunder Glas GmbH. The Bunder device is a single cylinder syringe wherein a fluid bypass allows mixing of the medicament solvent and medicament during operation of the device.
The multiple piston assemblies of the aforementioned devices are mechanically complex and expensive to manufacture. In addition, none of the aforementioned devices provides for the withdrawal of the used injection needle to reside completely within the device to afford safe disposal and disease prevention characteristics.
Another problem in the medical field is that of the communication of infectious diseases caused by used needles and syringes and fluids therefrom coming into contact with doctors, nurses, or other medical personnel. Needle tips often remain exposed after aspiration of a fluid or blood from a subject, or after injection of a medicine into a subject and medical personnel are sometimes accidentally pricked with such tips. This problem is particularly acute in situations where a syringe and needle have been contaminated with particularly virulent organisms such as the AIDS virus or the hepatitis virus. The risk of puncture with a contaminated needle point is of particular concern after an injection because a finger, hand or other part of the person administering the injection is typically in close physical proximity to the needle during its removal from the subject's tissue, during replacement of a needle or the needle cover or during removal of the needle from a syringe for disposal.
There is also danger of such exposures to personnel, such as maintenance people, other than medical personnel, when a used needle and/or syringe is laid aside or discarded with a needle tip still exposed. This danger continues even when a used needle and/or syringe are placed in a disposal container. For instance, it is a routine medical procedure to use a device which cuts off the tip of an exposed needle so that it may not be re-used. However, this procedure still leaves exposed needle stubs and syringe parts which may be contaminated with infectious agents and with which persons may come into contact and be infected. Thus, it is not uncommon for discarded needle stubs to protrude through plastic garbage bags or other containers and present serious risk of a puncture wound to a person handling or otherwise coming into contact with the container. Similarly, even after used needles are removed from syringes and placed in sealed containers, the exposed syringes must also be placed in sealed containers to reduce the likelihood of infectious contact with personnel. Sanitary disposal of used needles and used syringes is an expensive and time consuming process and entails significant risk of exposure to infectious disease vectors.
A related problem is that of the dangers of exposing a needle to the atmosphere prior to its being used in giving an injection or withdrawing a body fluid. Not only is there danger of wounds to user personnel and patients from the exposed needle tip, but also there is the danger that the exposed needle will become contaminated by airborne or aerosol borne microbial and other contaminants and infect the patient eventually injected. This danger is particularly acute in hospitals and other medical treatment areas where strains of antibiotic resistant microbes endemically contaminate the air and all exposed surfaces. Contact with non-sterile air is a certainty with conventional exposed needle syringe technology because, in this technology, needles are routinely exposed to the air or surfaces for some discrete amount of time during use. Also, in emergency use situations such as military combat, natural disasters, or industrial accidents, the unused needle may be left exposed to such contaminants by untrained, harried or inexperienced personnel.
An additional problem in the field is that of dosage management. For subjects who give themselves injections, either because they require regular doses of injected pharmaceuticals or because medical personnel are not available, it is critical to insure that dosages are correct. Diabetic subjects often find themselves in such situations, particularly diabetics who suffer from the related condition of blindness. Other blind people are similarly in need of a product which insures that both the type of medication and its dosage are correct for their specific needs. Similarly, soldiers in the field, travelers requiring regular injectable medications, and subjects in emergency situations where self-injection is necessary often have difficulty administering the proper dosage of a given drug and often have difficulty in using a conventional syringe. Such problems are also compounded by darkness or poor lighting conditions in battlefield, power failure, and other crisis or emergency situations.
Thus, it can be clearly seen that there is a need for injection devices which contain pre-measured dosages of particular pharmaceutical substances wherein the administration or self-administration of those doses can be easily and dependably achieved by non-professional personnel.